KnowraSchur's lemmaLinked fromLinked fromThe 6 pages that link to Schur's lemma, each with the reason it gives.All 6Related 4Compared with 2Irreducible representationRelated: It gives a powerful test for relations between irreducible representations.Character theoryRelated: It underlies the orthogonality relations that make characters useful.Maschke's theoremRelated: Once representations split into irreducibles, this lemma constrains maps between the pieces.Wedderburn–Artin theoremRelated: Endomorphism rings of simple summands become division rings in the classification.